Discover How the Polygraph Works: Scientific Technology at the Service of Truth

1.- Is the polygraph effective?

Absolutely. The polygraph remains the most advanced scientific technology in credibility assessment (lie detection). Although lies cannot be detected or measured in the same way as physical objects, countless studies confirm that with modern, evidence-based techniques, polygraph examinations achieve accuracy levels significantly higher than chance.

Modern polygraph instruments, supported by powerful computers, perform test administration, signal processing, and complex data analysis with a standard of consistency and revolutionary precision. Discover the science behind the search for truth.

2.- Myth: “The polygraph test is too subjective.

Reality: The testing and analysis processes in a polygraph examination are structured and standardized.

A polygraph test includes a structured or semi-structured interview where the examination topic and test questions are clarified and reviewed. The data acquisition and analysis phases are rigorous. Modern technology ensures the consistent application of validated polygraph techniques. For example, conducting the test using a standard automated voice and algorithmic means of analysis.

What Does It Record?

Cardio Cuff: Relative Changes in Blood Pressure

Pneumography: Changes in Movement Associated with Breathing

Electrodermal Activity: Changes in Skin Conductance or Resistance

Countermeasures: Subject’s motor activity – movements.

3.- Myth: Nervousness, stress, and anxiety can affect the test result.

Reality: The polygraph is not a detector of nervousness, stress, or anxiety. While these emotions are normal human reactions and understandable during the test, the polygraph goes beyond this.

Individuals with anxiety, which includes a variety of behavioral health symptoms, may benefit from professional help in this area. Fortunately, the polygraph focuses on a combination of physiological signals and psychological factors including emotion, cognition, behavioral experience, episodic memory, and more. The analysis and results of the polygraph are based on changes in physiological activity, in response to various presentations of test stimuli, compared to the individual’s physiological levels and normal physiological responses.

 4.- Are Polygraph Exams Legal?

Absolutely. The polygraph is a widely used legal investigative tool for establishing credibility in legal contexts and other types of investigations. Polygraph exams are always conducted with the consent of the examinee. While the admissibility of polygraph results in court depends on the laws of each state or province, numerous federal and state courts accept these results when both parties agree to their admissibility prior to the examination. Moreover, the use of polygraphs in government employee screening has been validated by the courts and successfully cited in defenses against claims of improper or negligent hiring.

5.- Myth: The polygraph test is biased against truthful examinees.

Reality: With modern testing and analysis methods, decision accuracy exceeds 90 percent, using scientifically validated techniques with a maximum of 4 relevant questions. Older polygraph methods prioritized sensitivity over test specificity, leading to criticism of bias against innocent people. However, modern polygraph methods, based on scientific evidence, are performed in an optimized manner to ensure unbiased sensitivity and specificity of the test.

6.- Where is the polygraph used?

The polygraph is used in many professions in criminal and investigative settings.

From law enforcement and intelligence agencies to the private examiner, the polygraph is used for a multitude of purposes. It is a powerful research tool to help establish credibility. In fact, the United States government alone employs up to 1,000 federally certified examiners.

More than 100 countries worldwide have approved the use of the polygraph, including all the superpowers. In Europe the use of the polygraph is spreading both at an official and private level. According to statistics from, it is estimated that in 2023 more than 16 million polygraph evaluations will be performed worldwide in sectors related to:

Law enforcement

Private examiners


intelligence agencies

7- Myth: An Internet search yields enough information to “beat a polygraph test.

Fact: Multiple scientific studies have proven that knowing information about the polygraph and execution of countermeasures is not sufficient for tampering with the exam.

Despite what Internet “experts” may say, evidence from these studies contradicts the effectiveness of any approach. More information about these studies is available from the American Polygraph Association and Europolygraph.

 8.- Myth: The polygraph cannot measure or detect lies.

Fact: All types of scientific tests rely on proxy signals and statistical methods that quantify things that cannot actually be detected or observed with deterministic perfection.

The polygraph works not because it can actually measure or detect lies, but because lying during a polygraph test is associated with subtle though predictable changes in physiological activity. And although all physiological activity is associated with multiple forms of human activity, many studies have shown that when using modern, evidence-based techniques, a polygraph examination can achieve accuracy rates that are significantly greater than chance.

Through ongoing research and education, Lafayette Instrument is dedicated to continuing scientific discovery and adoption in the polygraph community.

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